The use of sensing edges on doors is generally known. Sensing edges generally include a sheath having an area therein where at least a portion of a switch means is located. The switch means typically includes a pair of upper and lower, flexible, electrically conductive sheets, such as aluminum foil, positioned on the upper and lower sides of a perforated bridge. Upon application of external pressure to the sheath, the conductive sheets are deflected into electrically conductive engagement with each other through the perforations to thereby function as a switch to actuate suitable door control circuitry. The switch means could also include a fluid pressure sensitive switch element in which electrical contact is made or broken in response to pressure changes.
Generally, in switches of this type, there is required a highly localized deflection to operate the switch. Even a substantial force or weight may not be sufficient to actuate such a switch, if the force or weight is distributed over a large area. In an attempt to overcome this problem, such switches often include internal protrusions for locally enhancing internal forces reacting to an external weight. However, the use of internal protrusions added to the cost of the switch. Such switches were complex to manufacture and required additional raw materials to form the protrusions.
Consequently, a need has arisen for a highly sensitive switch which actuates a device upon a slight force being applied thereto. There further exists a need for a sensing edge which will respond to slight forces applied anywhere along the surface of the sheath, including forces acting on the sides of the sheath. Additionally, a need exists for such a highly sensitive switch which can be easily and readily manufactured without incurring prohibitive manufacturing costs.
The present invention is directed to a sensing edge for causing a closing door to open by actuation of a device upon force being applied to the sensing edge. The sensing edge of the present invention comprises a readily compressible sheath which imparts increased sensitivity to the sensing edge. In comparison to the prior art, device actuation is effected by a lesser force or weight and actuation occurs even where there is a less localized deflection.